Projector with adjustably positioned image plate

ABSTRACT

A projector is often positioned so that its optical axis is at an imperfect orthogonal angle with respect to a projection screen. This position causes a keystone distortion as well as imperfect focus in the projected image. To correct these undesirable problems, initially, a lens and/or an image-forming plate is independently repositioned to bring the projected image into focus based upon user input data. The keystone distortion is also corrected by redrawing the image on an image-forming surface based upon additional user input data.

FIELD OF THE INVENTION

The current invention is generally related to image projectors or imageprojection methods, and more particularly related to a correction of theprojected image when the optical axis of a projector is positioned at anon-perpendicular angle with respect to an image-projection surface.

BACKGROUND OF THE INVENTION

It is an important issue for screen projectors to project a digitallyformed image on a projection surface without any distortion. In priorart, a frequent problem for using a screen projector is a keystonedistortion associated with an imperfectly orthogonal angle between theprojection screen surface and an optical axis of the projector. In otherwords, the project is often positioned at an angle that is notperpendicular to the screen. In order to correct the keystonedistortion, the following prior art approaches have been proposed. Atypical prior art correction technique repositions the optical system orthe projector itself. In this technique, a lens is re-positioned to bein parallel with the image-forming plane, and this technique has beenembodied in a number of practical examples. Unfortunately, thistechnique requires a costly precision lens since an image is formed on awide-angle side. A second technique is to correct the distortion byadding a wedge-shaped lens and prism in the optical system. The secondtechnique also requires additional optical parts, and consequently, thesystem is costly for correcting a large amount of distortion.

Another prior attempt digitally corrects the keystone distortion inprojected images. A typical correction involves the projection of aknown test pattern in a fixed projection environment, and a digitalcamera takes an image of the projected pattern. Based upon the capturedimage, an amount of the distortion is calculated. An image-formingsource is positioned to compensate the distortion amount. Unfortunately,this prior solution requires a separate image-capturing device such as adigital camera.

In view of the above-described prior art, it remains desirable toprovide a projector that is equipped with an adjustable correctionmechanism for a user to easily correct distortions, which are caused bythe conditions under use and are different from expected distortions atthe design stage.

SUMMARY OF THE INVENTION

In order to solve the above and other problems, according to a firstaspect of the current invention, a method of projecting an image,including: projecting an image-forming surface onto an image-projectionsurface by a projector, the image-forming surface containing an image,an optical axis of the projector being positioned at a non-perpendicularangle with respect to the image-projection surface; inputting focus datato adjust focus; and mechanically adjusting an angle of an image-formingcomponent of the projector with respect to the image projection surfacebased the focus data, the image-forming component including a lens andan image-forming plate, wherein the image is focused on theimage-projection surface.

According to a second aspect of the current invention, a system forprojecting an image, including: an optical unit for projecting animage-forming surface onto an image-projection surface by a projector,the optical unit including an image-forming component, the image-formingsurface containing an image, an optical axis of the image-formingcomponent initially being positioned at a non-perpendicular angle withrespect to the image- projection surface; an input unit connected to theoptical unit for inputting focus data to adjust focus; and an angleadjustment unit connected to the image-forming component formechanically adjusting an angle of the image-forming component withrespect to the image projection surface based the focus data, whereinthe image is focused on the image-projection surface.

These and various other advantages and features of novelty whichcharacterize the invention are pointed out with particularity in theclaims annexed hereto and forming a part hereof. However, for a betterunderstanding of the invention, its advantages, and the objects obtainedby its use, reference should be made to the drawings which form afurther part hereof, and to the accompanying descriptive matter, inwhich there is illustrated and described a preferred embodiment of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one preferred embodiment of the projector accordingto the current invention.

FIG. 2 is a cross-sectional view illustrating positional relationshipsamong components in one preferred embodiment of the projector accordingto the current invention.

FIG. 3 is a cross-sectional view illustrating positional relationshipsamong the components of the preferred embodiment of the projectoraccording to the current invention after the image plate is moved to anew position.

FIG. 4 shows a relation between a point (X,Y) on an image-forming plateor surface and a point (x,y) on an image-projection surface.

FIG. 5 illustrates a method of measuring an equal line segment.

FIG. 6 is a prospective view illustrating one preferred embodiment ofthe image plate angle adjusting or moving unit according to the currentinvention.

FIG. 7 is a flow chart illustrating acts involved in a preferred processof focusing the projector according to the current invention.

FIG. 8 is a block diagram illustrating one preferred embodiment ofhardware components for digitally correcting an image in the projectoraccording to the current invention.

FIG. 9 illustrates an example of a standard image pattern.

FIG. 10 illustrates an exemplary conversion using four pairs ofcoordinates.

FIG. 11 illustrates an exemplary distortion correction display whichincludes a cursor and arrows which surround the cursor.

FIG. 12 is a flow chart illustrating acts involved in a preferredprocess of correcting distortion in a projected image according to thecurrent invention.

FIG. 13 is a flow chart illustrating acts involved in an alternativeprocess of inputting coordinates for correcting distortion in an imageprojected by the projector according to the current invention.

FIG. 14 is a block diagram illustrating a second preferred embodiment ofthe projector system according to the current invention.

FIG. 15 is a block diagram illustrating a third preferred embodiment ofthe image-correcting projector according to the current invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring now to the drawings, wherein like reference numerals designatecorresponding structure throughout the views, and referring inparticular to FIG. 1, one preferred embodiment of the projector 100according to the current invention includes an optical component 101, animage plate 102, an optical axis moving unit 103, a supporting element104, an image plate angle control unit 105, an input unit 106 and acentral processing unit (CPU) 107. The projector 100 projects an imageonto an image projection surface. The optical component 101 comprises aseries of lenses for forming an image generated by the image plate 102such as a liquid crystal display (LCD). The optical axis moving unit 103moves the optical axis of the optical component 101 towards the centerof the image projection surface. The supporting element 104 supports theimage plate 102 by at least two predetermined points, and the imageplate angle control unit 105 controls the supporting element 104 so thatthe angle of the image plate 102 is adjusted with respect to the imageprojection surface. The input unit 106 inputs position coordinate valuesso that the focus of the image is adjustably corrected on the imageprojection surface. The CPU-107 runs a predetermined program to controlthe optical axis unit 103, the image plate angle control unit 105 andthe input unit 106. The predetermined program is stored in media such asa hard disk, a floppy disk, read only memory (ROM) and random accessmemory (RAM). In an alternative embodiment of the projector 100, theoptical axis of the optical component 101 is fixedly positioned, and theoptical axis moving unit 103 is eliminated.

Now referring to FIG. 2, a cross-sectional view illustrates positionalrelationships among an image plate I 204, an optical component 202, animage-projection surface or projection surface 200 and a light source206 in one preferred embodiment of the projector according to thecurrent invention. The image plate I 204 projects via the opticalcomponent 202, an image on the projection surface 200 which extends froma point A at one end to a point B at the other end. The light source 206is located behind the image plate I 204 for providing light. Since thevertical axis of the lens 202 and that of the image plate 204 asindicated by the dotted lines are at an angle with respect to the imageprojection surface 200, the image formed on the image projection surface200 is not focused and has undesirable distortion. This relationship isalso indicated by an angle formed by an optical axis 208 and the imageprojection surface 200. In other words, the optical axis 208 is at anon-perpendicular angle with respect to the image projection surface200. To adjust the focus, the optical axis 208 of the optical component202 is rotated by the optical axis moving unit 103 of the projector 100as shown in FIG. 1. This focus mechanism replaces a prior opticalcomponent that requires a wide-angle lens and/or a prism. Despite theabove rotation, it is not possible to bring both the point A and thepoint B into focus at the same time since these points have a differentdistance to the image plate I 204. The correction is made as will bedescribed below.

Now referring to FIG. 3, a cross-sectional view illustrates positionalrelationships among the image plate 204, the optical component 202, theimage projection surface 200 and the light source 206 of the preferredembodiment of the projector according to the current invention after theimage plate 204 is moved to a new position. In order to simultaneouslyfocus the points A and B of an image on the image projection surface200, the image plate I 204 is moved. That is, an end of the image plateI 204 correspondingly forming a point A in the image is moved closer tothe optical component 202 at a position 204 A while the other end of theimage plate I 204 is fixedly positioned. The above description pertainsto a general concept of correcting the image distortion according to thecurrent invention.

To farther illustrate the above concept of the image correction,equations are used. The image projection surface is expressed by thefollowing equation (1):

z=px+qy+c  (1)

where the z axis is an optical axis of the optical component and isperpendicular to the image plate while the x axis and the y axis areboth parallel to the image plate surface and are perpendicular with eachother. c is a constant. The image plate is assumed to be positioned atz=1 between the optical component and the image projection surface. Thisassumption is often used in the area of the camera projection system.

The coordinate values on the image projection surface are expressed by(x,y) while those on the image plate are expressed by (X,Y). FIG. 4shows a relation between a point (X,Y) on the image plate and a point(x,y) on the projection surface without the z axis coordinate takinginto account. That is, a point (X,Y) on the image plate is projectedonto a point$\left( {\frac{cX}{1 - {pX} - {qY}},\frac{cY}{1 - {pX} - {qY}},\frac{c}{1 - {pX} - {qY}}} \right)$

on the same projection surface which includes the z axis coordinate.From the above relationship, equations (2), (3) and (4) are derived whenX is zero, Y is zero and X and Y are zero.

(0,Y) projected to (0, −c/q, −c/q Y)  (2)

(X,0) projected to (−c/p, 0, −c/p X)  (3)

(0,0) projected to (0, 0, c)  (4)

The distance between (0,Y) and (X,0) on the image plate becomes thefollowing distance on the image projection surface: $\begin{matrix}{{\frac{c}{q}\sqrt{1 + \frac{\left( {{qY} + 1} \right)^{2}}{Y^{2}}}} \cong {\frac{c}{q}\sqrt{1 + \frac{1}{Y^{2}}}}} & (5)\end{matrix}$

Alternatively, the same distance on the image projection surface isexpressed: $\begin{matrix}{{\frac{c}{p}\sqrt{1 + \frac{\left( {{pX} + 1} \right)^{2}}{X^{2}}}} \cong {\frac{c}{p}\sqrt{1 + \frac{1}{X^{2}}}}} & (6)\end{matrix}$

Thus, then X=Y, the ratio of the distance is:

K=p/q  (7)

Since a unit of distance is the focal length of an image-forming lens,

−1<X,Y<1  (8)

−1<<p, q <<1  (9)

Equations (8) and (9) are held true. Furthermore, the horizontal andvertical axes on the image plate are also assumed to be on the sameplane as those on the image projection plane. With the aboveassumptions, a coefficient of an equation expressing a screen is solvedby measuring an equal line segment on the image projection surface interms of the length on the image plate. In other words, a horizontalline and a vertical line of the same length are projected as lineshaving a ratio p:q.

Now referring to FIG. 5, a method of measuring an equal line segment isillustrated. Assuming p≦q, a horizontal line and a vertical line of theequal length are projected onto an image projection surface. Thevertical line is projected as a line op while the horizontal line isprojected as oq. One way to determine the ratio p/q is that a user movesa pointer of a pointing device to a point q′ on the horizontallyprojected line oq to indicate a line portion oq′ that has the same linelength as the vertically projected line op. The coordinates of the pointq′ is stored in the image plate angle control unit 105 as shown in FIG.1. The ratio K as shown in Equation (7) is thus determined by the abovemeasurement. Using the ratio K, Equation (1) is now expressed as:

z=Kqx+qy+c=q(Kx+y)+c  (10)

Since Equation (10) defines a plane whose contour lines are expressed byKx+y=cos t, the equations for light on the image projection surface andthe image plate surface are in parallel to the above contour lines.Thus, since the ratio of the inclined direction cosine with respect tothe image projection surface is 1:k, the ratio with respect to the imageplate is also 1:k in order to maintain the image-forming relationbetween the image projection surface and the image plate.

Referring to FIG. 6, a prospective view illustrates one preferredembodiment of the image plate angle adjusting or moving unit accordingto the current invention. The preferred embodiment includes a set offour actuators 601, 602, 603 and 604 which are located on a base board600. These actuators 601-604 adjustably tilt the image plate I at adesirable angle with respect to the image projection surface. There isno limitation as to the number of the actuators. The amount of the tiltor incline is expressed by:

1/{square root over (K²+1+L )}  (11)

or

K/{square root over (K²+1+L )}  (12)

The absolute value of the inclined angle or the actual focus is adjustedby confirming an image projected on the image projection surface as itdepends on the distance to the image projection surface. The absoluterotated angle is an angle formed by the image plate at I and that at I′as shown in FIG. 3. In comparison to the focal length of animage-forming lens, the image projection surface is generally locatedfurther and its angle is approximately zero. Consequently, the imageplate angle control needs to adjust the angle only in a small amount.

Now referring to FIG. 7, a flow chart illustrates acts involved in apreferred process of focusing the projector according to the currentinvention. In act S701, the optical axis is moved or rotated to projectan image at a desired position. A predetermined horizontal line segmentand a predetermined vertical line segment are projected onto aprojection surface in act S702. In act S703, it is determined whether ornot it has been specified a point on a longer one of the above two linesegments to match the length. One way to specify the point is to use apointing device. It is waited in the act S703 until the point isspecified. When the point is specified in the act S703, the parameterp:q is calculated based upon the coordinates of the specified point instep S704. The image plate is angled based upon the calculated parameterp:q in step S705. After the image plate is angled, it is determinedwhether or not the image is focused on the image projection surface instep S706. If the focus is not appropriate in the act S706, thepreferred process goes back to the act S703. On the other hand, if thefocus is appropriate, the horizontal/vertical line segment is taken outof display in act S707. The preferred process ends.

Now referring to FIG. 8, a block diagram illustrates one preferredembodiment of hardware components for digitally correcting an image inthe projector according to the current invention. A projector 800includes an optical component 801 comprising a plurality of lenses, animage plate 802 such as a liquid crystal display for forming aprojection image, an image forming unit 803 for forming an image for theimage plate 802, a correction unit 804, a calculation unit 805, and aninput unit 806 for inputting positional coordinates for correctingkeystone distortion in the projected image, a standard pattern imageformation unit 807 for forming a standard image and a central processingunit (CPU) 808. The CPU 808 runs a program that is stored in media suchas read-only memory (ROM), random access memory (RAM), a hard disk and afloppy disk and control the image forming unit 803, the correction unit804, the calculation unit 805 and the input unit 806. To start thecorrection, the standard pattern image formation unit 807 projects apredetermined standard pattern.

Now referring to FIG. 9, an example of a standard image pattern isillustrated. The exemplary standard image pattern includes a knownparallelogram ABCD and a known eclipse E inside the parallelogram ABCD.If the optical axis of the projector according to the current inventionwere perpendicular to the image projection surface, the figures would beprojected as a rectangle A′B′C′D′ and a circle E′ on the imageprojection surface as indicated by the dotted lines under idealconditions. To use the predetermined standard image pattern, an operatorof the projector points out four corners or coordinates by a pointingdevice or a keyboard, and these selected four positions specify thecoordinates of the four corners of the ideally projected rectangleA′B′C′D′. When a keyboard is used, the coordinate values are typed in orthe cursor position is moved by arrow keys. Similarly, a circle E isused to specify an amount of distortion in the projection, and thecircle tends to show distortion more readily.

The relationship between the coordinates before and after the correctionis expressed in the matrix equation below: $\begin{matrix}{\begin{pmatrix}\begin{matrix}x^{\prime} \\y^{\prime}\end{matrix} \\w^{\prime}\end{pmatrix} = {{\begin{pmatrix}t_{11} & t_{12} & t_{13} \\t_{21} & t_{22} & t_{23} \\t_{31} & t_{32} & 1\end{pmatrix}\begin{pmatrix}\begin{matrix}x \\y\end{matrix} \\1\end{pmatrix}} = {T \cdot \begin{pmatrix}\begin{matrix}x \\y\end{matrix} \\1\end{pmatrix}}}} & (13)\end{matrix}$

where the coordinates before correction (x,y) and the coordinates aftercorrection (x′,y′). w′ is a predetermined parameter while T is aconversion matrix. By providing the above four pairs of cornercoordinates, Equation (13) is solved for the conversion matrix T. Afterthe conversion matrix T is determined, all other points in the image arecorrected based upon the same conversion matrix T to correct distortionbefore projecting them onto the image projection surface.

Now referring to FIG. 10, an exemplary conversion is illustrated usingfour pairs of coordinates. Before the conversion or correction, the fourpairs of coordinates A, B, C and D are respectively shown as (0, 0), (0,800), (1000, 8000) and (1000, 0). When these four corner coordinates arespecified in the above described manner, the corrected coordinates arerespectively specified as (0,0), (120, 600), (700, 600) and (750, 50).Using these corresponding sets of coordinates, the conversion matrix isdetermined for correcting the distortion.

In an alternative embodiment, another operational method for digitalcorrection, the projector initially displays a menu including an imagesize and a video input channel. An operator selects desirable conditionsfor the projector. In addition to the above selections, the initial menualso includes a distortion correction display. FIG. 11 illustrates anexemplary distortion correction display which includes a cursor 1101 andarrows which surround the cursor. The cursor is movable in response to apointing device or other input devices that are connected to theprojector input terminal. By moving the cursor to four desirablecoordinates to specify an amount of distortion as described with respectto FIG. 9. For example, the four corner coordinates A′, B′, C′ and D′are respectively inputted (100, 800), (100, 100), (1000, 100) and (1000,800). As described above, the coordinate value of the cursor 1101 arealternatively inputted via a keyboard. The input process can be guidedby a menu.

In any case, the numerical coordinate values have the unit of pixels.The projector keeps track of the address indicating the coordinate ofthe cursor 1101 in the liquid crystal display (LCD). The coordinatevalues of points x′, y′, x and y are obtained based upon Equation (13)where x′ and y′ are inputted by a user while x and y are determined bythe projector. By the same token, four sets of two pairs of coordinatesare obtained and designated as (x′₀, y′₀), (x₀, y₀), (x′₁, y′₁), (x₁,y₁), (x′₂, y′₂), (x₂, y₂), (x′₃, y′₃), (x₃, y₃). These coordinates areused in Equation (13) to solve the conversion matrix T. Since thecoordinates inputted by the correction unit 803 into the image formationunit 803 are (x′, y′), the x, y coordinates are determined by thefollowing equation based upon the inverse conversion matrix T⁻¹:$\begin{matrix}{\begin{pmatrix}\begin{matrix}x \\y\end{matrix} \\1\end{pmatrix} = {T^{- 1}\begin{pmatrix}\begin{matrix}x^{\prime} \\y^{\prime}\end{matrix} \\w^{\prime}\end{pmatrix}}} & (14)\end{matrix}$

Now referring to FIG. 12, a flow chart illustrates acts involved in apreferred process of correcting distortion in a projected imageaccording to the current invention. In act S1201, a standard imagepattern is projected onto an image projection surface. In act S1202, itis determined whether or not any one coordinate is inputted for apredetermined number of representative points. For example, thepredetermined number is the above described four sets of two pairs ofcoordinates. If there is one input, it is determined whether or not thenumber of inputted coordinates has reached the predetermined number inact S1203. The acts 1202 and 1203 are repeated until the predeterminednumber of coordinates is reached. When the predetermined number ofcoordinates is reached, the conversion matrix is determined based uponthe inputted coordinate values in act 1204. The conversion matrixrepresents distortion or an amount of correction. Subsequently, an imageis corrected in act S1205 using the matrix determined in the act S1204.The corrected image is projected back onto the image projection surfacein act S1206. It is further determined whether or not the distortion inthe re-projected images is desirably corrected in act S1207. If thedistortion correction is okay, the standard image pattern is removed inS 1208, and the preferred process ends. On the other hand, if thedesirable distortion correction is not achieved, the preferred processreturns to the act S1202.

Now referring to FIG. 13, a flow chart illustrates acts involved in analternative process of inputting coordinates for correcting distortionin an image projected by the projector according to the currentinvention. An interactive window such as shown in FIG. 11 is displayedin act S1301. In act S1302, it is determined whether or not a cursor inthe interactive window has moved to a predetermined first corner. If thecursor has moved towards the first predetermined corner, it is waiteduntil coordinate values are inputted for the first corner in act S1303.On the other hand, if the cursor has not moved towards the first corner,the alternative process waits in the act S1302. Similarly, acts S1304through S1309 are sequentially performed to obtain the predeterminedsecond, third and fourth coordinates are obtained the correspondingcorners. In other words, unless the sequentially determined coordinatesare obtained in a predetermined order, the alternative process does notproceed to a next act. The above described alternative process is usedin lieu of the acts S1202 and S1203. The above-described preferredprocess efficiently corrects the keystone distortion or the imageprojection surface based upon the user inputted coordinates.

Now referring to FIG. 14, a block diagram illustrates a second preferredembodiment of the projector system according to the current invention.In contrast to the first preferred embodiment as shown in FIG. 1, thesecond preferred embodiment separates the projector 1400 from adistortion correction unit 1450. The projector 1400 further includes anoptical unit or an optical component 1401 having a plurality of lenses,an image forming unit 1402 such as a liquid crystal display (LCD) and asupport unit 1403 having at least two supporting points for supportingthe image plate 1402. The distortion correction unit 1450 furtherincludes an optical axis move data output unit 1451 for outputtingoptical axis move data specifying the movement of the optical axistowards the center of the image projection surface. Similarly, thedistortion correction unit 1450 further includes an image plate anglecontrol data output unit 1452 for outputting data to control the supportunit 1403 so that the angle of the image plate 1402 is changed withrespect to the image projection surface. The distortion correction unit1450 also includes an input unit 1453 for inputting projectioncoordinate values to be used in focusing an image. A central processingunit (CPU) 1454 runs a predetermined program stored in storage mediasuch as a read only memory (ROM), a random access memory (RAM), a floppydisk and/or a hand disk. The program generates signals to instruct theoptical axis move data output unit 1451, the image plate angle controldata output unit 1452, and the input unit. The first preferredembodiment performs the acts described in the flow chart as shown inFIG. 7. An alternative embodiment of the image correcting projectorsystem according to the current invention has a fixed optical axis, andthe distortion correction unit 1450 needs no optical axis move dataoutput unit.

Now referring to FIG. 15, a block diagram illustrates a third preferredembodiment of the image correcting projector according to the currentinvention. The third embodiment includes a projector 1500 and an imagecorrection unit 1550. The projector 1500 further includes an opticalcomponent 1501 comprised of a plurality of lenses and an image plate1502 such as a LCD for forming an image. The projection image correctionunit 1550 further includes an image forming data output unit 1551, acorrection unit 1552, a calculation unit 1553, an input unit 1554 and astandard image forming data output unit 1555. Since the correction unit1552, the calculation unit 1553 and the input unit 1554 aresubstantially identical to the corresponding units 804, 805 and 806 asdescribed with respect to FIG. 8, the descriptions of these units arenot repeated. The third preferred embodiment includes the standard imageforming data output unit 1555 which outputs standard image data to theimage forming data output unit 1551. The third preferred embodimentperforms the acts described with respect to the flow chart in FIG. 12. Acentral processing unit (CPU) 1556 controls the above-described units1551 through 1554 via software. The software is stored in any one of theabove-described media or is down loaded via the Internet.

It is to be understood, however, that even though numerouscharacteristics and advantages of the present invention have been setforth in the foregoing description, together with details of thestructure and function of the invention, the disclosure is illustrativeonly, and that although changes may be made in detail, especially inmatters of shape, size and arrangement of parts, as well asimplementation in software, hardware, or a combination of both, thechanges are within the principles of the invention to the full extentindicated by the broad general meaning of the terms in which theappended claims are expressed.

What is claimed is:
 1. A method of projecting an image, comprising thesteps of: projecting the image contained in an image plate to form aprojected image on an image-projection surface via an optical component,an optical axis of the optical component being positioned at anon-perpendicular angle with respect to the image-projection surface;inputting predetermined focus data for adjusting focus of the projectedimage on the image-projection surface; and mechanically adjusting aparameter selected from the group consisting of the optical axis of theoptical component and a tilting angle of the image plate with respect tothe image-projection surface based on the predetermined focus data,whereby the projected image is focused on the image-projection surface;collecting keystone correction data for ultimately correcting keystonedistortion in the projected image; determining a conversion matrix basedupon the keystone correction data for correcting the image contained inthe image plate; correcting the image on the image plate based upon theconversion matrix to substantially eliminate the keystone distortion;and projecting the corrected image on the image plate onto theimage-projection surface.
 2. The method of projecting an image accordingto claim 1 wherein the optical axis of the optical component withrespect to the image-projection surface is independently adjusted. 3.The method of projecting an image according to claim 1 wherein thetilting angle of the imaging plate with respect to the image-projectionsurface is independently adjusted.
 4. The method of projecting an imageaccording to claim 1 wherein the predetermined focus data is collectedby projecting a predetermined image containing vertical and horizontalline segments with equal lengths on the image projection surface to formthe projected image containing respective projected vertical andhorizontal line segments, and wherein a ratio in length between theprojected vertical and horizontal line segments is determined, the ratiobeing the predetermined focus data.
 5. The method of projecting an imageaccording to claim 1 wherein the keystone correction data includes apredetermined number of pairs of coordinates of an image of apredetermined shape and corresponding pairs of coordinates of aprojected image of the predetermined shape.
 6. A system for projectingan image onto an image-projection surface to form a projected image,comprising: an optical component having an optical axis, the opticalaxis initially being positioned at a non-perpendicular angle withrespect to the image-projection surface; an image plate located nearsaid optical component for forming the image, the image being projectedon the image-projection surface via the optical component; an input unitconnected to said optical component and image plate for inputtingpredetermined focus data for adjusting the projected image in focus onthe image-projection surface, wherein said input unit further collectskeystone correction data for ultimately correcting keystone distortionin the projected image, an angle adjustment unit connected to saidoptical component and said image plate for mechanically adjusting aparameter selected from the group consisting of the optical axis of saidoptical component and a tilting angle of said image plate with respectto the image-projection surface based on the predetermined focus data,whereby the projected image is focused on the image-projection surface;a calculation unit connected to said input unit for determining aconversion matrix based upon the keystone correction data; and acorrection unit connected to the calculation unit for correcting theimage on the image plate based upon the conversion matrix tosubstantially eliminate the keystone distortion in the projected image.7. The system for projecting an image according to claim 6 wherein saidoptical component further includes a lens.
 8. The system for projectingan image according to claim 7 wherein said angle adjustment unitindependently adjusts an optical axis of said lens with respect to theimage projection surface.
 9. The system for projecting an imageaccording to claim 7 wherein said angle adjustment unit independentlyadjusts the tilting angle of said image-forming plate with respect tothe image projection surface.
 10. The system for projecting an imageaccording to claim 6 wherein said input unit collects the predeterminedfocus data by projecting a predetermined image containing vertical andhorizontal line segments with equal lengths on the image-projectionsurface to form a projected image containing respective projectedvertical and horizontal line segments, and wherein a ratio in lengthbetween the projected vertical and horizontal line segments isdetermined, the ratio being the predetermined focus data.
 11. The systemfor projecting an image according to claim 6 wherein said keystonecorrection data includes a predetermined number of pairs of coordinatesof an image of a predetermined shape and corresponding pairs ofcoordinates of a projected image of the predetermined shape.